1. In rabbit and cat retinas, synaptic interactions involving GABA-ergic amacrine neurons mediate certain specific types of ganglion cell receptive fields. In both species, GABA synaptic circuitry generates the antagonistic center-surround receptive fields off Y-type ganglion cells; in the rabbit, BAGA amacrine cells also generate direction - and orientation-selective fields. Two questions concerning retinal organization may then be asked. First, which neurons are involved in the formation of these defined receptive fields; second, what is the detailed synaptic circuitry through which these neurons exert their effects? Methods for the specific localization of GABA neurons will be used to answer these questions. Immunocytochemical localization of glutamate decarboxylase, combined with autoradiographic localization of uptake - and receptive-sites for GABA, will be used for the specific visualization of GABA neurons in the inner plexiform layer. A morphometric analysis of synaptic connectivity of GABA neurons will be carried out in both species using these techniques. The long-range goal of these studies is an understanding of the detailed synaptic mechanisms underlying specific information-processing circuits in the visual system, such as those respobsible for complex and hypercomplex receptive fields. 2. The hypothalamic peptide somatostatin serves as a neuroeffector in the central nervous system, and is present in mammalian retina. Two questions will be asked regarding its function in this tissue. First, what is the subcellular distribution of somatostatin within retinal neurons; second, does somatostatin function as a transmitter per se, or as a local hormone? Localization of somatostatin and of its receptors, using novel immunohistochemical methods, will be carried out to answer these questions; they represent the first step towards a detailed understanding of the roles of neuropeptides in retinal function.